The discovery of endogenous NO in exhaled air, and its use as a diagnostic marker of inflammation dates back to the early 1990 (See e.g. WO 93/05709; WO 95/02181). Today, the significance of endogenous NO is widely recognised, and since a few years back, a clinical analyser is available on the market (NIOX®, the first tailor-made NO analyser for routine clinical use with asthma patients, AEROCRINE AB, Solna, Sweden).
In the summer of 1997 the European Respiratory Journal published guidelines (ERS Task Force Report 10:1683-1693) for the standardisation of NO measurements in order to allow their rapid introduction into clinical practice. Also the American Thoracic Society (ATS) has published guidelines for clinical NO measurements (American Thoracic Society, Medical Section of the American Lung Association: Recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide in adults and children—1999, in Am J Respir Crit Care Med, 1999; 160:2104-2117). The NIOX® analyser for clinical use, and others mainly intended for research applications, are based on chemiluminescence determination of NO. While highly accurate and reliable, chemiluminescence determination of NO requires an advanced apparatus involving an ozone generator, a vacuum pump, means for dehumidification of the exhaled air, to mention only a few examples. Although the chemiluminescence analysers have developed significantly, they are still rather expensive and bulky.